1. Field of the Invention
The present invention relates generally to a scroll type compressor. More specifically, the present invention relates to an improved mechanism for suppressing noise generated by an orbiting scroll member as it rotates around a fixed scroll member to generate compressed gas.
2. Description of the Related Art
Conventional scroll type compressors generally include a standard structure having two offset scroll members. Both scroll members have spiroidal or involute spiral members attached to a circular end plate. The spiroidal members are interfitted and nestled with each other so that as an orbiting scroll member rotates around a fixed scroll member a gas chamber is formed by the interfitting spiroidal members. During the course of the orbiting scroll's rotation, the volume and location of the gas chamber is defined by the interfitting scroll members and decreases as the rotation progresses. Gas introduced into the gas chamber is compressed when the gas chamber decreases in volume according to the progression of the rotating spiral member. Japanese Examined Patent Publication No. 59-215984 discloses a compressor of this type herein generally described by reference to FIGS. 13 through 17. As shown in FIG. 13, a fixed scroll 112 is secured by bolts to housing 111 and comprises a base plate 112a integrally formed with a perpendicularly connected spiral member 112b. At the front side of the housing 111, an eccentric shaft 114 is operably connected to a rotary shaft 113 at a predetermined radial distance from the axis of the shaft 113. A bushing 115 is likewise rotatably supported by the eccentric shaft 114. An orbiting scroll 117 is operably connected to the bushing 115, via radial bearings 116. The orbiting scroll 117 includes a base plate 117a, a spiral member 117b perpendicularly connected to the plate 117a, and a generally cylindrical shaped boss 117c integrally formed with the plate 117a at the rear surface of the plate 117a. The boss 117c is fitted on to the bushing 115. As shown in FIG. 15, both spiral members 112b and 117b are interfitted and nestled with each other so as to define gas chambers P wherein at least two points of contact are defined between surfaces 112b and 117b. Each compression chamber P is defined by the interfitting spiral members 112b and 117b together with the base plates 112a and 117a.
When the rotary shaft 113 rotates, the eccentric shaft 114 moves in a circumference such that the distance between a center axis line O.sub.1 and a center axis line O.sub.2 forms a radius r.sub.1 of rotation of shaft 114 as shown in FIG. 16. Since the eccentric shaft 114 is separated from the center axis line O.sub.3 (i.e., same center axis line of the orbiting scroll 117) by a predetermined distance, the orbiting scroll 117 moves such that the distance between the center axis line O.sub.1 of the rotary shaft 113 and a center axis line O.sub.3 of bushing 114 is a radius r.sub.2. During the course of the orbiting motion of the scroll 117, the volume and location of the each compression chamber P, defined by the interfitting spiral members, decreases from the outer to inner portions thereof as shown in FIG. 15. Refrigerant gas is compressed in this manner when a particular amount of gas within the compression chamber P decreases in volume according to the progression of the moving spiral member 117b. The compressed refrigerant gas is then discharged through a discharge port 112c which is formed at a center portion of the base plate 112a into a discharge chamber.
Unfortunately with conventional scroll type compressors, the rotation of the rotary shaft 113 produces a tendency in orbiting scroll 117 to rotate around its own axis (hereinafter referred to as self rotation). This tendency produces a corresponding decrease in the ability of the compressor to efficiently compress gas. Given this tendency, it is highly desirable to limit or prevent the self rotation of the orbiting scroll 117. As shown in FIG. 13, an anti-self-rotation mechanism 118, disposed between the base plate 117a of the scroll 117 and the inner front surface of the housing 111, is designed to prevent the self rotation of the scroll 117. In addition, the mechanism 118 functions to transmit the compression reaction force from the scroll 117 to the inner wall of the housing 111. Mechanism 118 also functions to set the maximum radius r.sub.2 for the rotation of the scroll 117.
A center of gravity of the orbiting scroll 117 lies on the center axis line O.sub.3 rather than on the center axis line O.sub.1 of the rotary shaft 113 due to the design of the eccentric shaft 114. Thus when the scroll 117 rotates, the centrifugal force produced by the rotation creates a condition where scroll 117 becomes dynamically unbalanced. To compensate for this unbalancing, a balancing weight 119 is integrally connected to the bushing 115. This weight generates a counter centrifugal force that opposes or cancels the centrifugal force acting on the scroll 117.
The spiral member 112b of the fixed scroll 112 slidably abuts against at least two inner and outer portions of the spiral member 117b. As illustrated in FIG. 15, the abutting portions T, between the spiral members 112b and 117b, move from the outer sides of the spiral members to the central portions thereof. If the portions T are able to advance in their rotation without a separation occurring between abutting members, the compression chambers P can be maintained with desirable air-tight seals.
Normally, the manufacturing and design tolerances allowed between fixed and orbiting scrolls 112 and 117 prevent the spiral members 112b and 117b from being damaged due to any occasional and abnormally high pressure generated in either compression chamber P. However, if the orbital radius r.sub.2 of the scroll 117 were to be fixed, the urging force of the spiral member 117b against the spiral member 112b would be insufficient to maintain an adequate seal between spiral members 112b and 117b. Consequently, a mechanism for automatically adjusting the orbital radius r.sub.2 of the scroll 117 is disposed between the rotary shaft 113 and bushing 115. This allows the orbit of scroll 117 to be shifted by a predetermined amount in order to maintain a sufficient force and consequent seal between spiral members 112b and 117b.
The mechanism for adjusting the radius r.sub.2 will now be described with reference to FIGS. 16 and 17. In FIG. 17, an adjusting pin 120 is connected to the bushing 115 which corresponds to the center axis line O.sub.3 of the bushing 115. The pin 120 is inserted into an adjustment hole 121 formed in the rotary shaft 113 with clearance C.sub.1 developed therebetween to allow the pin 120 to reciprocate in a perpendicular direction with respect to the axial direction of the bushing 115.
That is, as shown in FIG. 16, the center axis line O.sub.3 of the bushing 115 is reciprocative within the predetermined angle .theta. along the circular locus of radius r.sub.1 even though center axis line O.sub.2 of the eccentric shaft 114 is the center of rotation for bushing 115. As the pin 120 moves within the hole 121, as shown in FIG. 16, the radial distance between the axis line O.sub.1 of the rotary shaft 113 and the axis line O.sub.3 of the bushing 115, alternates between radius r.sub.21 and radius r.sub.22. As a result, the urging force acting between the slidably abutting portions T can be adjustably controlled to allow for proper sealing between members 112b and 117b and consequently, for the efficient operation of the compressor.
To prevent bushing 115 from disengaging from the shaft 114, a snap ring 122 is fitted to the tip portion of the eccentric shaft 114 as shown in FIG. 17. Clearance C.sub.2 permits the bushing 115 and balancing weight 119 to shift along the axial line O.sub.2 of the eccentric shaft 114. As a result, when the scroll 117 rotates, the bushing 115 and the balancing weight 119 reciprocate along the axial line of the eccentric shaft 114 due to the presence of the clearance C.sub.2. This movement generates noise. When such a conventional scroll type compressor is employed in vehicular air conditioning systems, it is desirable to minimize the noise caused by shifting of bushing 115 and balancing weight 119. Reducing the noise in this way, tends to increase the comfort level of the vehicle's driver and passengers.